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I'm so used to seeing the "fish crawling onto the shore" cartoon of evolution that I assumed the branching always went that way - land creatures are branchoffs of sea creatures. But surely this is oversimplified - are there examples in the other direction, where a branching occured in land animals and one branch then returned to the sea?



I think all marine mammals fit this, right?


Yes. And for a non animal example, there's sea grass, which evolved from land grasses.


And for an animal but non-mammal example, there are penguins.


Sea snakes, as well.


And sea turtles, and I guess iguanas are a kind of sea lizard.


> iguanas are a kind of sea lizard

Only the marine iguanas, but yes.

Also salt-water crocodiles (the largest living reptile).


Mangroves are aquatic trees that evolved from regular land trees.


Sea grass is a monocot but belongs to a different order (Alismatales) than true grass (Poales).


Thanks for the correction. Interesting


Whales.

https://baleinesendirect.org/en/discover/life-of-whales/morp...


Also ichthyosaurs' ancestors were terrestrial reptiles, though the whole branch is now extinct.


Not an animal, but many marine algae descend from freshwater algae, possibly because the last Snowball Earth event may have wiped out the marine algae by covering the oceans with ice (while freshwater algae survived in structures like cryoconites, tiny freshwater puddles that form on glaciers).

https://www.youtube.com/watch?v=D0R3FVTLvT0

(People who know their taxonomy will notice that I'm conflating algae and cyanobacteria, mea culpa.)


There are also lots of extinct examples like Ichthyosaurs, Mosasaurs, Plesiosaurs

Modern examples are saltwater crocodiles, sea turtles or sea snakes


> Hyraxes have highly charged myoglobin, which has been inferred to reflect an aquatic ancestry.[20]


Interesting thing about the evolution of Hyraxes is that it is likely to be an example of a Hard Polytomy - as in Hyraxes, Elephants and Manatees split off simultaneously


I knew that Hyraxes were related to elephants, And I've seen rock hyraxes in the wild many times, but TIL the term "Hard Polytomy" https://en.wikipedia.org/wiki/Polytomy


Hippos come from the whale branch. https://en.m.wikipedia.org/wiki/Whippomorpha


Hippos don't come from the whale branch, but they share a branch with whales. From wikipedia:

> It is unknown whether the last common ancestor of whales and hippos led an aquatic, semiaquatic/amphibious, or terrestrial lifestyle

However, whales are a great example of a clade that went land -> water in their evolutionary history.


Sloths (formely): https://en.wikipedia.org/wiki/Thalassocnus


Whales are the first example that springs to mind.


Time for the aquatic ape hupothesis https://en.m.wikipedia.org/wiki/Aquatic_ape_hypothesis


Marine mammals.


Sea mammals.




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